The major objective of this research proposal is to improve our understanding of the molecular organization of bone and bone-like tissues, including dentin. The basic strategy is to first study tissues, which for one reason or another have some "natural" peculiarities which can help unravel the complexities of this problem. This information will be compared with so-called "normal" bones and in the final stage of the program, with diseased bones. The focus will be on the distribution of crystals and their relations to the collagen fibril in mature bone as well as during development. Particular attention will be directed to late stages of mineralization in which crystals apparently grow into a fused aggregated state. Individual collagen fibrils, both mineralized and unmineralized, from turkey tendon and fish bone will initially be studied in the transmission electron microscope (TEM) embedded in thin films of vitreous ice. This provides a unique means of examining the structure of unstained, unfixed and hydrated collagen itself as well as the first stages of mineralization. The aggregated state does not occur in these two tissues. We will primarily address the question of how the collagen structure can accommodate the observed intrafibrillar crystal organizational pattern. Unsually dense bones such as the tympanic bulla of the whale will then be examined, as these are composed almost entirely of fused crystal aggregates. Stages of aggregate formation will be studied in bones that naturally do not remodel, such as those of certain aquatic mammals. A key question to be addressed is whether aggregates form between fibrils or within fibrils. The results of all this work will be compared with "normal" bones from calf, rat and human, which also contain a significant proportion of fused aggregates. We will study one or several diseased states of bones in order to try to detect changes in their molecular organization as compared with "normal" bone. The analytical tools of our studies will include SEM, TEM in the image and diffraction modes, X-ray diffraction, Fourier Transform Infrared spectroscopy and biochemical characterization of matrix components of the organic matrices. Knowledge of the molecular organization of bone should form the basis for understanding its formation, its role during calcium homeostasis, its destruction during remodeling and its biomechanical functions as a structural support system.